Tires for use in the winter season to travel over snowy and icy roads include studded tires, studless tire and tires fitted with steel tire chains. Studded tires have been required to provide good grip performance on frozen roads but because of the extensive wear they cause on pavement and on account of the resulting dust particles, regulations are being adopted to ban the use of studded tires.
More recently, studless tires have been developed in an effort to improve the low-temperature characteristics of tread rubber so that its grip performance will be comparable to that of studded tires. However, the performance of such studless tires on frozen roads is somewhat inferior to that of studded tires. A further problem with studless tires is that in order to provide improved low-temperature characteristics, softening agents such as ester-based plasticizers and naphthenic plasticizers have to be incorporated in large amounts, so that during extended use or storage, the plasticizers may be partly lost and deteriorated to cause an increased hardness in the tire tread; in other words, the performance of an aged studless tire on ice is inferior to that of a virgin tire. Because of these reasons, studless tires have not yet been fully commercialized.